The present invention relates generally to an instantaneous frequency measurement (IFM) receiver.
In an IFM receiver, delay lines and correlators are used to measure the frequency of input signals. If the delay time is .tau., and the angular frequency of the input signal is .omega. (=2.pi.f), the outputs of the correlators are sin .omega..tau. and cos .omega..tau.. An IFM receiver has a wide input bandwidth with fine frequency resolution. The conventional approach to achieve such a design is to use multiple delay lines. A very common relation among the delay lines is .tau., 2.tau., 4.tau., 8.tau., 16.tau., 32.tau., and 64.tau. where .tau. represents the shortest delay line. In the above design, there are a total of seven delay lines. The short delay lines are used to resolve ambiguity. The shortest delay line must satisfy .delta..omega..tau.&lt;2.pi. where .delta..omega. is the bandwidth of the receiver. The longest delay line is used to produce the fine frequency resolution.
United States patents by applicant James B. Y. Tsui sole or et al for IFM and other EW receivers include (1) U.S. Pat. No. 4,194,206 issued Mar. 18, 1980 for an Instantaneous Frequency Measurement (IFM) Receiver With Capability to separate CW and pulsed Signals; (2) U.S. Pat. No. 4,336,541 issued Jun. 22, 1982 for Simultaneous Signal Detector for an Instantaneous Frequency Measurement Receiver; (3) U.S. Pat. No. 4,426,648 issued Jan. 17, 1984 for Simultaneous Signal Detection for an IFM Receivers by Detecting Intermodulation Products: (4) U.S. Pat. No. 4,547,727 issued Oct. 15, 1985 for Simultaneous Signal Detection for IFM Receivers by Transient Detection; (5) U.S. Pat. No. 4,633,516 issued Dec. 30, 1986 for an Instantaneous Frequency Measurement Receiver With Digital Processing; (6) U.S. Pat. No. 4,200,840 issued Apr. 29, 1980 for a Dual Detection Scheme for Compressive Receivers; and (7) U.S. Pat. No. 4,644,267 issued Feb. 17, 1987 for a Signal Analysis Receiver With Acousto-Optic Delay Lines. There is also an application (by Shaw, Tsui & Hedge) Ser. No. 07/215,662 filed July 6, 1988, for PSK Detection Using an IFM Receiver. These patents and application are hereby incorporated by reference.
Other U.S. patents of interest are U.S. Pat. No. 3,939,411 to James, which teaches an IFM system capable of measuring pulse signals of differing frequencies emitted by a single source. U.S. Pat. No. 4,532,515 to Cantrell et al teaches a device for measuring AOA by converting received echos to complex numbers representing the amplitude and phase. U.S. Pat. No. 4,638,319 to Chua teaches a RF system wherein a phase comparison means provides a signal output and bearing angle.